Sighting mechanism



DEHIWH nuum April 1951 F. v. JOHNSON SIGHTING MECHANISM Filed Nov. 4,1942 3 Sheets-Sheet l Inventor. FrithioF Johnson, y w

l-hs Attorneg.

3EARGH ROOM April 24, 1951 F. v. JOHNSON 2,550,482

SIGHTING MECHANISM Filed NOV. 4, 1942 3 Sheets-Sheet 2 InventofFTi'thiO'F Johnson,

i5 Attorneg April 24, 1951 F. v. JOHNSON sxsmme MECHANISM 5 Sheets-Sheet3 Filed Nov. 4, 1942 r m m 0 6 mcMZ M #5 J *M l a M O ..n w r n o w r a.w m Kw nh .w 1 FH I F s Patented Apr. 24, 1951 b'tillibnf fiuum SIGHTINGMECHANISM Frithiof V. Johnson, Scotia, N. Y., assignor to GeneralElectric Company, a corporation of New York Application November 4,1942, Serial No. 464,453

6 Claims. (01. 3349) This invention relates to sighting mechanism, moreparticularly to sighting mechanism for use in the control of gunfire,and it has for its object the provision of improved mechanism of thischaracter.

While it is applicable more generally in the control of gunfire, thisinvention is especially useful in the control of the fire of machineguns at rapidly moving targets, such as aircraft. And it relates ingeneral to the type of sighting mechanism described and claimed in mycopending application, Serial No. 459,780, filed September 26, 1942,Patent 2,467,831, granted April 19, 1949, and which is assigned to thesame assignee as the present invention.

The sighting mechanism of that application controls the gun so as togive it the correct lead angle with relation to the line of sight to thetarget as required bythe speed of the target. The present inventionlikewise controls the gun to give it the correct lead as required by thespeed of the target, but in addition it superimposes an elevation leadcorrection as required by the gun elevation and the range to the target.This correction I will refer to as superelevation.

In accordance with this invention, a sight is provided for establishinga line of sight to the target. The sight is mounted upon a support whichis movable so that the line of sight may be brought to bear on thetarget and follow it. And the support itself is caused to move in arigid system with the gun which is controlled.

Also mounted upon the-support is a gyrosco which is free to move about apredetermind point of suspension. The gyroscope is coupled to thesupport so that these members may be moved relatively to each other, butthe coupling means is constructed and arranged to apply a torque to thegyroscope which is proportional to the magnitude of the displacementbetween the gyroscope and the support and which tends to precess thegyroscope to bring its spin axis into a predetermined position withreference to the support. When the support is moving in order to causethe line of sight to follow a target, the gyroscope will be displacedfrom this predetermined relative position by an amount dependent uponthe sped of the target, and also upon the strength of the coupling meansbetween the gyroscope and the support.

The coupling effect between the gyroscope and the support is controlledto give the gun the correct lead as is made necesary by the speed of thetarget, and this is accomplished by controlling the torque generated bythe coupling means in accordance with the time of flight of theprojectile from the gun to the target.

In addition, the sighting device of this invention includes means forchanging the position of the gyroscope in elevation with reference tothe support so as to introduce the correction for superelevation,referred to above.

In one form of this invention, the gyroscope is displaced in thevertical planewith reference to its support by an amount required by gunelevation and target range by the application of a torque to thegyroscope gimbal system. This torque is varied in accordance with afunction of the angle of elevation of the gun.

Therefore, in keeping the line of sight on the target in elevation, thesuperelevation lead correction is automatically generated and applied tothe gun.

For a more complete understanding of this invention, reference should behad to the accompanying drawings in which Fig. 1 is a side elevation,mainly in section, illustrating a sighting device embodying thisinvention; Fig. 2 is an end elevation of the sighting device of Fig. 1,the major portion of the figure being shown in section; Fig. 3 is an endelevation view of a part of the sighting device of Figs. 1 and 2 takenthrough the line 3-3 of Fig. land looking in the direction of thearrows, the figure being drawn to a larger scale than Figs. 1 and 2;Fig. 4 is a sectional view taken through the line 4-4 of Fig. 1 andlooking in the direction of the arrows, the figure being drawn to alarger scale than Fig. 1; Fig. 5 is a perspective view of a portion ofan optical system used in the sighting device of Figs. 1-4; Fig. 6 is adiagrammatic representation of certain control elements for thegyroscope elements of the sighting device; and an electrical powersystem therefor; Fig. 7 is an elevation view illustrating therelationship of the sighting device to a gun and how it is connectedwith the gun; Fig. 8 is adiagrammatic view of certain elements of thesighting mechanism illustrating the functioning of these elements; Fig.9 is a diagrammatic representation of a field of battle; and Fig. 10 isa diagrammatic view illustrating a modification of a part of thissighting mechanism.

Referring to the drawings, this invention has been shown in one form inconnection with a sighting device I 0 intended to be used in' thecontrol of a machine gun H, and intended to determine for any firingproblem the gun lead angle made necessary by the speed of the target.

and the superelevation, which is required by the gun tlevation and therange to the target. In the specific embodiment shown, the machine gunII is mounted for use from the ground against aircraft targets; and itis mounted so that it may be moved both in train and in elevation withreference to the support. As shown in Fig. 7, the gun is mounted upon asuitable turntable 42 mounted upon a fixed base l5; so that it may bemoved in train about a VertiLal axis. Also, it has trunnions l4 aboutwhich it may be elevated on a horizontal axis.

The sighting device comprises a metallic casing l5 defining a chamberi6, and a casing section I! depending from the casing l5 and defining achamber [8.

Mounted within the chamber I6 is a gimbal ring 19 rotatably supported byshafts 20 and 2!. Pivoted to the gimbal ring l9 to move about an axis atright angles to the suspension axis of the ring is a gyroscope 24; thering is provided with shafts 25 which are received in bearings (notshown) mounted in the gyroscope. Mounted within the casing of thegyroscope is the gyroscope wheel shaft 21, which shaft is driven by anysuitable high-speed motor (not shown), but which preferably will be athree-phase induction motor. The motor also is housed by the gyroscopecasing. As will be understood, the axis of the shaft 21 constitutes thespin axis of the gyroscope.

The shaft 21, as shown, projects from the one end of the gyroscopecasing, and On its projecting end it carries an eddy current disk 28.The eddy current disk comprises a plate-like disk 29 which is rigidlysecured to the shaft 27 and which carries a second plate 30 having anouter curved surface approximately in the form of a segment of a spherewhich has its center in the center of suspension of the gyroscope. Spunover the curved surface of this member is an electrically conductingsheet 3|, which preferably will be made of copper. Positioned oppositethe eddy current disk 28 is a suitable electromagnetic device 32 fixedlymounted in the adjacent wall of the casing 15. The magnet 32 comprises acentral pole 33 and an outer annular pole 34 between which is insertedthe magnet energizing coil 35. The magnet 32 is mounted in the casing 15so that the longitudinal axis of the center pole piece 33 passes throughthe center of suspension of the gyroscope; and the lengths and shapes ofthe pole pieces 33 and 34 are such that their ends lie on a sphericalsurface having a center at the center of suspension of the gyroscope.

The eddy current disk 28 and the magnet 32 constitute a coupling betweenthe gyroscope and the casing I5 which applies a torque to the gyroscopewhich tends to precess it into alignment with the axis of the magnet. Itwill be understood that in the operation of the coupling, when the eddycurrent disk 28 is rotated in the magnetic field set up by the magnet,and the axis of the gyroscope is aligned with the axis of the magnet noeddy currents are induced in the disk. However, if the axis of themagnet departs from the axis of the disk, the motion of the disk underthe magnetic poles causes eddy currents to flow in the copper sheet 3|.A resulting electromagnetic force acts on the gyroscope which tends toprecess it into alignment with the magnets axis. The magnitude of thisrestoring force varies directly with the angle of departure between thegyroscope and the magnet, and with the coefficient of coupling which isa function of the magnet excitation current. This excitation of themagnet is controlled by means of a suitable rheostat 36 (Fig. 6) whichis provided with a manually operable setting knob 31.

The operation of the coupling may better be understood by reference toFig. 8. This is a diagrammatic view and is a plan of the gyroscope andmagnet with an angular displacement AB between them. The eddy currentdisk 28 is assumed to spin clockwise viewed from the magnet, the portionof the disk at p, directly under the center pole of the magnet, istravelling upwardly perpendicular to the plane of the figure. The motionof this part of the disk in the field of the magnet causes eddy currentsto be induced in the disk. These currents interacting with the fieldwhich produces them, causes a retarding force to act on the disk at thepoint p in a downward direction. This force constitutes a torque aboutthe spin axis of the gyroscope and also about the horizontal axis 26-26.The torque about the spin axis tends to slow the spin axis, but suchslowing is prevented by the electrical power supplied by the gyroscopemotor. The torque about the axis 26--26 causes precession about avertical axis, that is, precession in the plane of the figure, whichtends to bring the gyroscope into correspondence with the magnet. Thelinear speed of the disk through the magnetic field increases as A5increases, while the torque arm remains substantially constant, wherebythe precession rate varies substantially directly with A13, and with thesquare of the magnetic field.

Therefore, it will be observed that the gyroscope will follow the motionof the magnet in the horizontal plane. In exactly the same way, thegyroscope will follow the motion of the magnet in elevation should themagnet be displaced in elevation with reference to the gyroscope.

The gyroscope is intended to control the line of sight of the sightingmechanism, and it is connected to a suitable optical system so that theline of sight remains parallel to the gyroscope axis.

The optical system controlled by the gyroscope is constructed andarranged to establish a collimated line of sight parallel to the axis ofthe gyroscope. This optical system is mounted within a tubular member 38depending from the casing section l'l. It comprises a reticule 39secured in a fixed position in the tube 38. The reticule 39 is formed ofglass and has its upper side 39a silvered. In this silvered side isscribed a Cross 40 simulating cross hairs. Mounted in the tube 38 belowthe reticule 39 is a source of light 4|, shown as an incandescent lamp.The light passing through the cross 40 is focused by the collimatinglens 42. And in passing through this lens all of the light rays from anysingle point on the reticule are made parallel. The collimated lightnext strikes an inclined glass 43 which is mounted in the chamber I8.This glass 43 is carried by a fork-like extension 44 of the gimbal ring[9 so that it rotates with the gyroscope about the axis of suspension ofthe ring I9. It is also connected with the gyroscope by an angle halvinglinkage 45, which is connected by a pin 45a with the gyroscope and a pin45b with the glass 43, :0 as to rotate about an axis parallel to theaxis of movement of the gyroscope in the gimbal ring l9 through one-halfthe angle made by the gyroscope; the distance frcm the axis 25-26 of thegyroscope to pin 45a is substantially one-half the distance from theaxis of rotation of the mirror 43 in the extension 44 to the pin 45b sobti-itibi'i nuulw that the mirror moves on this axis through butone-half of the angle of movement of the gyroscope about axis 2926.Therefore light from the center of the reticule 39 striking the glass 43is reflected parallel to the gyroscope axis. An observer looking intothe reflecting glass will at all times see the center of the crosslines, and the center of the cross lines will move about in the field ofview as the gyroscope moves about relative to its casing l5.

It will be observed that the two walls 46 and 41 of the casing 17opposite the two inclined faces respectively of the glass 43 are formedof glass so that the observer may look directly through the chamber l8and the transparent glass 43 to view the reticule image, and also toview the target. The observer will be stationed at the right-hand sideof the chamber, as viewed in Fig. 1, his eye being indicated in thislocation.

It will be observed, therefore, that the optical system'generates alighted reticule which may be viewed in the field of view of the target,and it will be further understood that in the operation of the s ght itis the purpose of the observer to bring the reticule image onto thetarget, and to keep it on the target.

The sighting mechanism is connected with the gun i I so that the centralaxis of the magnet 32 always remains parallel with the bore of the gun;that is, so that when the spin axis of the gyroscope is aligned with theaxs of the magnet, the spin axis and the line of sight will be parallelto the bore of the gun. For this purpose, the sighting mechanism 19 isconnected with the gun by means of a parallelogram linkage comprising alink 43 having one end rigidly connected with the gun trunnions so as tobe swung with the gun, a link 49 which has one end pivoted to the link48 and its other end pivoted to the casing 15, and further, rigidhorn-like supports 50 pivotally secured to a fixed standard 5|. Thisstandard 5| is secured to the gun turntable [2 by means of columns 52 soas to move with the gun in train. As the gun elevates to some position,indicated in dotted lines in Fig. '7, the link 58 turns with the gunabout the axis of trunnions I4. The motion of the end of the link 48 istransmitted through link 49 to the sght casing which turns about thepivot at 5! to the dotted line position, as shown in. Fig. '7. In viewof the connections between the sighting mechanism I0 and the gun. itwill be understood that the central axis of the magnet 32 will be heldin fixed parallel relation with the bore of the gun, and will move withit irrespective of the motion given the gun in-train and elevation.

The gyroscope 24 is also controlled by means of an unbalanced weight 53which is mounted within the chamber Hi. This weight is mounted upon anarm 54 which in turn is secured to one side of a face gear 55. This facegear, as shown, is mounted to rotate in a bearing 56 which is supjortedupon a fixed bracket 5'! in the chamber IS. The face gear meshes with apinion 5S fixed to the upper shaft 29 of the gimbal ring l9. The weightand face gear thus are pivoted to move on a horizontal axis which isparallel to the axis of the gun trunnions Id. The weight applies throughthe face gear and pinion 58 a torque to the gmbal I9 in such a directionas to cause the gyroscope to precsss in such a way as to depress theeddy current disk 29.

It will be observed that when the Inc of sight is horizontal, the effectof the moment of the weight on the ring l9 will be a maximum, and

when the line of sight is directly vertical the effect will be zero.This is as it should be, because if the target be in the horizontalplane of the sight, then for a given range the gun must be elevated to ahigher angle than for any other position of the target to compensate forthe effect of gravity in the trajectory of the projectile. The otherextreme condition is when the target is directly above the sight; underthese conditions, the gun will be directed straight at it, andsuperelevation will be zero-neglecting, of course, differences in therelative speed of the target and the sight.

On the end of the gyroscope opposite the eddy current disk 28 is anutation damper. This damper comprises an annular weighted ring 59 whichis pivoted on an inner flexible ring 60 by means of pivot pins 6!located in a diameter of the rings, as more clearly shown in Fig. 3. Thering 60 is pivoted to the gyroscope casing 24 by means of pins 62 tomove on an axis passing through a diameter at right angles to the axisof movement of the ring 59. The pins 6] and 62 are in the form of screwsand they are adjusted so that a predetermined resistance to motion isset up between the two rings and between the inner ring and the casing.Nutational motions of the gyroscope produce relative motions between thetwo rings and between the inner ring and casing. The frictional forcesso produced cause the nutation to be damped. Stops 63 are provided toengage the weighted ring 59 to limit its movement, the stops providingsome impact damping.

The nutation damper just described is not a part of this invention, butis that of Charles S. Grimshaw, and it is described and claimed in thiscopending application, Serial No. 487,309, filed May 7, 1943, Patent2,412,453 granted D..- cember 10, 194.6, and which application isassigned to the same assignee as this invention.

Also, the gyroscope is provided with a suitable caging device 64provided with a control knob 65 for caging and releasing the gyroscope.

The electrical diagram for the sighting mechanism is illustrateddiagrammatically in Fig. 6. Electrical power for the system is suppliedfrom a battery 66. A dynamotor 61 functions to convert the directcurrentof the battery to three phase alternating current for the threephase induction motor of the gyroscope 24. The gyroscope motor isstarted by closing a switch 68. The lamp M is connected to the directcurrent source 66 and is controlled by means of a switch 69, and itsintensity is controlled by an adjustable resistance 10. The magnet 32and its controlling resistance 36, as shown, are connected to thebattery 66 through switch 68.

In the operation of the sighting mechanism, it will be assumed that thegyroscope is rotating to rotate the eddy current disk 28 and that themagnet 32 is energized. Also, it will be assumed that the lamp 4! isenergized. The observer will view the target through the transparentwindows 46' and 41, and the transparent reflecting glass 43. Also, theobserver will view the image of the reticule 39 in the field of view ofthe target. The gun I I is moved in train and in elevation to move thecasing l5 so as to bring the image of the reticule onto the target andto cause the image to remain on and follow the target as the targetmoves in space.

When the casing I5 is thus moved with the gun, the axis of the gyroscopewill lag behind the casing by an amount which is dependent upon thespeed of the casing, and the coupling coeflicient between the gyroscopeand the casing, that is, between the eddy current disk 28 and the magnet32. The speed of the casing l5, of course, measures the angular velocityof the target, and the coupling coefficient is adjusted by theresistance 36 in accordance with the time of flight of the projectilefrom the gun to the target so that the lag in the position of thegyroscope axis behind the support is the correct lead angle for thegum-neglecting for the moment the effect of the weight 53 on thegyroscope that is, it is the correct lead for the gun, as required bythe speed ofthe target; the rheostat 36 is graduated in terms of range,and preferably a range scale, graduated in hundreds of yards, will beprovided to assist the observer in setting the time of flight knob 3'!of the rheostat.

The displacement of the gyroscope with reference to its casing I5 isimparted to the line of sight because of the motion imparted to theglass 43 by the gyroscope. Therefore, in order to keep the reticuleimage on the target, the position of the gun II, which is fixed to thecasing l5, necessarily will have to be advanced with reference to theline of sight by an angle equal to the angle of lag of the gyroscopebehind the casing l5, and this angular advance of the gun will be itscorrect lead, as required by the speed of the target.

The unbalanced weight 53 functions to generate superelevation, which aspointed out previously, is the correction to be applied to the gun inelevation which is required by the range of the target and its positionin the elevation plane. This weight, as previously pointed out,functions to depress the gyroscope with reference to the magnet, andthereby in bringing the reticule image back on the target the observerwill necessarily generate superelevation and apply it to the gun.

The operation of the sighting mechanism may be better understood byreference to Fig. 9. Here the target is following an inclined courseABC. The gunner moves his gun II in such a manner as to keep the line ofsight established by the illuminated reticule on the target. The spinaxis of the gyroscope 24 will also be directed toward the targetbecause, as has been described, the

optical system is arranged to make the line of sight parallel to thegyroscope axis.

The line of sight is shown making an angle [3 with a fixed base line 0Ain the plane of target travel OAC. AB is the lead angle made necessaryby the velocity of the target along ABC, and a is the superelevationangle. The elevation of the gun is denoted eg. The pivot axis 202| ofthe gyroscope gimbal l9 lies in vertical plane OED, and is inclined atan angle so from the vertical. The magnet axis lies along the bore ofthe gun.

The lead angle AB can be found with good accuracy from the expression BAB T dt where T is time of flight of the projectile corresponding topresent range, and

is the angular velocity of the target.

It can also be shown that the superelevation correction is closelyrepresented by o'=KT cos eg 8 where K is a constant depending on theballistics of the projectile. That is, a" varies with the cosine of theelevation of the gun and is nearly a linear function of the time offlight corresponding to the present range of the target.

Torques from two sources act to precess the gyroscope in following thetarget. The first of these arises in the eddy current coupling device.The eddy current disk 28 is shown turning counter-clockwise as viewedfrom the magnet. The portion of the disk directly under the center poleat the magnet is traveling in a direction perpendicular to plane OBD.The eddy currents induced in the disk by its motion in the magneticfield interact with the field to produce a retarding force, shown as F,which is also directed perpendicular to plane OBD; but in a directionopposite the motion. This force constitutes a torque about the spin axisof the gyroscope and also about axis qq, in plane GED, and passingthrough the axis of suspension of the gyroscope. The torque about thespin axis tends to slow the spin of the gyroscope, but such slowing isprevented by the electrical power supplied to the motor. The torqueabout axis qq is shown as vector Q, the direction of which indicates theaxis about which the torque acts, and the length of which indicates themagnitude of the torque. The speed with which the disk passes under themagnet depends on the magnitude of angle DOB, so that force F increasesas angle DOB increases. Since the moment arm of F about axis qq remainsessentially constant, the torque Q also increases as angle DOBincreases. By properly prc-portioning the thickness of the conductingsheet 3| on the eddy current disk 28, the torque Q is made to varydirectly with angle DOB. Torque Q also varies with the square of theflux density under the magnet, and this is controlled by the rheostat 3Bwhich is set in accordance with present range to the target. The torqueQ is therefore Q=C (angle DOB) (square of flux density) where C is aconstant depending on the design of the sight.

The second source of torque acting on the gyroscope is thesuperelevation weight. This, through the combination of face gear 55 andpinion 58 applies a torque R to the gyroscope about the pivot axis ofthe gyroscope gimbal, which axis is perpendicular to the gun bore andlies in a vertical plane OED. The magnitude of R varies with the cosineof the elevation angle eg of the gun. This will be seen from the factthat when the gun bore is horizontal, the weight projects horizontallyand exerts its maximum torque on the gimbal, whereas when the gun boreis vertical the weight is pointed upward and exerts no torque on thegimbal. The torque applied by the weight may thus be expressed as R=Mcos eg where M is a constant depending on the weight and the gear ratioat the face gear and pinion combination.

It is well known that under the action of a torque such as Q, thegyroscope will precess in such a direction as to tend to align itselfwith the torque; and further that if two torques such as Q and R actsimultaneously the rate at which the gyroscope moves can be found byvectorial addition of the rates due to the torques separately. Since thegyroscope precesses in plane OBC to follow the target it is evident thatthe resultant of torques Q and R must lie in plane 0130. In other words,the superelevation torque R tends C (angle DOB) (square of fiux density)Angular momentum of spin The scale of rheostat 36 is calibrated to makethe magnet flux such that Angular momentum of spin T when range R is seton the scale. angular rate produced by torque Q is Angle DOB T This maybe resolved into two components of velocity,

Then the AB p 77 in plane OBC and T in plane OCD But the velocity of thegyroscope in plane CEO is whence @4 dt T B AB- T This is the desiredsolution for the lead angle. As has previously been described, the ratein plane GOD is exactly equal to and opposite that produced by thesuperelevation weight,

which is M cos eg Angular momentum of spin Thus a M cos eg T angularmomentum of spin u'=T cos e g angular momentum of spin However, thedesired value is a'=K T cos 69 which is obtained if the moment of thesuperelevation weight is made M ,=K (angular momentum of spin) =constantFrom examination of the above analysis it will be seen that in order tocause the gyroscope and the line of sight to move with the target, thegunner must lead the target by an angle which depends directly onangular velocity. Furthermore, the longer the range set on the rheostat36 the weaker is the flux of the magnet and the greater must be the leadangle toproduce a given angular velocity. The additional effect of thesuperelevation weight causes the gyroscope to tend to precess downwardfrom the target; and the operatorin order to compensate for the down=ward precession will elevate the gun, and hence the magnet, until theadditional upward rate which it produces compensates for the downwardrate due to the superelevation weight. Further it will be seen that thelonger the range and the weaker the magnet flux, the greater must be theupward displacement of the gun to effect this compensation, and thegreater will be the superelevation produced.

Small variations from the desired result M cos so will occur whenthe'gimbal ring l9 rotates about its axis TT. The result of this is tocause the weight 53 to rise or drop through-a small angle. The errorresulting from this rise or fall may be made quite small by making theratio between the large gear 55 and the small gear 58 quite large.

If it be desired to increase the accuracy of the mechanism, the momentrM may be varied by using a sliding weight, as shown more clearly inFig. 10. Here, the sliding weight H is mounted upon an arm 12 projectingfrom the large gear 13 which corresponds to the gear 55. This gear 13 isgeared to a gimbal ring 14 corresponding to the gimbal ring [9 through agear 15 corre sponding to the gear 58. The weight II is positioned bymeans of a cord 16 and a spring TI. The cord is wrapped over a cam 18,the position of which is adjusted inaccordance with a function ofadvance range Ba and present range R. That is, the moment M of theabove-mentioned equation:

must be equal to the superelevation function for the advance range ofthe target, as determined from suitable range stages (which range is thetargets range at the instant of impact with the projectile) timesangular momentum of spin and divided by the time of flight T of theprojectile for present target range.

What I claim as new and desire to secure by Letters Patent in the UnitedStates is:

1. Gun sighting mechanism comprising means for establishing a line ofsight, a gyroscope connected to said means so that the direction of saidline of sight is always in fixed relation to the direction of the spinaxis of the gyroscope, said gyroscope controlling the direction of saidline of sight in accordance with the position thereof, means mountingsaid line of sight establishing means and said gyroscope movable withthe gun as it is moved in space in order to cause said line of sight tofollow a target, means on said movable means for applying to saidgyroscope a precessing torque to cause it to tend to follow saidlast-named means as it is moved to cause said line of sight to followthe target and for controlling said torque so that the position of saidgyroscope with reference to said last-named means measures the leadangle of the gun required by the speed of the target, and additionalmeans connected to said gyroscope for applying to it a precessing torquein accordance with the range of the target and elevation of the gun todisplace the gyroscope spin axis with reference to said last-named meansso that a correction in elevation is applied to said gun.

2. Sighting mechanism for a gun comprising sighting means forestablishing a line of sight, a gyroscope, means connectingsaidgyroscope to 11 said sighting means so that the gyroscope spin axisand said line of sight are always in parallel- 1 ism and so that thegyroscope controls the direction of said line of sight, a mount for saidsighting means and gyroscope movable in train and elevation in order tocause said line of sight to 7 follow a target, said gyroscopecontrolling the di- 1 rection of 'said line of sight in accordance withits Y position relative to said mount, coupling means between said mountand gyroscope applying a torque to said gyroscope in order to cause itto precess to tend to follow said mount as the mount moves in keepingsaid line of sight on the target, means controlling the coupling effectof said coupling means in accordance with the range of the target, andadditional means connected to said gyroscope for applying a torque to itto cause its spin axis to be displaced in a vertical plane withreference to said mount by an amount which is a function of the range ofthe target.

3. Sighting mechanism for a gun comprising sighting means forestablishing a line of sight, a

gyroscope, means connecting said gyroscope to said sighting means sothat the gyroscope spin axis and said line of sight are always inparallelism and so that the gyroscope controls the direction of saidline of sight, a mount for said sighting means and gyroscope movable intrain and "elevation in order to cause said line of sight to follow atarget, said gyroscope controlling the direction of said line of sightin accordance with its position relative to said mount, coupling meansbetween said mount and gyroscope applying a torque to said gyroscope inorder to cause it to precess to tend to follow said mount as the mountmoves in keeping said line of sight on the target, means controlling thecoupling effect of said coupling means in accordance with the range ofthe target, and an unbalanced weight connected to the gyroscope so as toapply a torque to it to cause it to precess its spin axis verticallywith reference to said mount by an amount which is a function of theelevation of said gun and mount, and to the range of said target.

4. Sighting mechanism for a gun comprising sighting means forestablishing a line of sight, a gyroscope, having gimbal ring supportmeans, means connecting said gyroscope to said sighting means so thatthe gyroscopes spin axis and said line of sight are always inparallelism and so that the gyroscope controls the direction of saidline of sight, a mount for said sighting means and gimbal rin supportmeans movable in train and elevation in order to cause said line ofsight to follow a target, said gyroscope controlling the direction ofsaid line of sight in accordance with its position relative to saidmount, coupling means between said mount and gyroscope applying a torqueto said gyroscope in order to cause it to precess to tend to follow saidmount as the mount moves in keeping said line of sight on the target,means controlling the coupling eilect of said coupling means inaccordance with the time of flight of the projectile to the target, andan unbalanced weight connected to a predetermined 65 one of the gimbalaxes of said gimbal ring support means for applying a torque to thegyroscope to displace its spin axis in the vertical direction withreference to said mount by an amount which is a function both of theangle of elevation of the gun and the time of flight of said projectile.

5. Sighting mechanism for a gun comprising a sight for establishing aline of sight to a target, a support for said sight, a gimbal ring onsaid support mounted for rotation on a nominally and generally verticalaxis, a gyroscope in said ring mounted for movement on an axis at rightangles to said vertical axis and with its spin axis generallyhorizontal, connection means between said gyroscope and sight so thatthe direction of said line of sight is always in parallelism with thespin axis of said gyroscope and is controlled in accordance with theposition of said gyroscope with reference to said support, said supportbeing movable in train and elevation so as to keep the line of sight ona target, an electromagnetic coupling between said support and saidgyroscope for applying to said gyroscope a precessing torque to cause itto tend to align itself in a predetermined position with reference tosaid support, means controlling the magnetic coupling effect of saidcoupling in accordance with the time of flight of a projectile to saidtarget, and an unbalanced weight connected to said gimbal ring to applythereto a torque about its axis of movement which torque is a functionof the position of said support in elevation and also of the time offlight of said projectile.

6. Sighting mechanism for a gun comprising sighting means forestablishing a line of sight, a gyroscope, means connecting saidgyroscope to said sighting means so that the spin axis of the gyroscopeand said line of sight are always in parallelism and so that thegyroscope controls the direction of said line of sight, a mount for saidsighting means and gyroscope movable in train and elevation in order tocause said line of sight to follow a target, said gyroscope controllingthe direction of said line of sight in accordance with its positionrelative to said mount, connection means between said mount andgyroscope for causing a displacement between said gyroscope and saidmount which is a function of the angular velocity of said mount and therange of said target, and additional means connected to said gyroscopeto displace it with reference to said mount by an amount which is afunction both of the angle of elevation of said mount and of the rangeof said target.

FRITHIOF V. JOHNSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,936,442 Willard Nov. 21, 1933FOREIGN PATENTS Number Country Date 616,248 Germany Aug. 1, 1935Certificate of Correction Patent No. 2,550,482 April 24, 1951 FRITHIOFV. JOHNSON It is hereby certified that erg-or appears in the rintedspecification of the above numbered patent requirmg correction as f0ows:

Qolumn 6, line 65, for 46' read 46; column 9, lines 83 and 84, for theequatxon read gand that the said Letters Patent should be read ascorrected above, so that tha same may conform to the record of the casein the Patent Ofiice.

Signed and sealed this 21st day of August, A. 11 1951.

THOMAS F. MURPHY,

Assistant Oommz'asiam of Fannie.

